Spark plug with shuttle electrode

Abstract

A spark plug with shuttle electrode is provided for an internal combustion engine which includes a combustion chamber in which a main charge diluted with a neutral gas is ignited, the spark plug housing a lamination cavity in which a central electrode opens and in which a lamination injector is able to inject under pressure a pilot charge consisting of an easily flammable combustive-AF fuel mixture, the cavity being connected to the combustion chamber by a lamination duct, while a shuttle electrode is interposed between the central electrode and a ground electrode and can translate in the lamination duct.

The invention claimed is: 
     
       1. A spark plug with shuttle electrode ( 1 ) for an internal combustion engine ( 2 ), said spark plug ( 1 ) comprising at least electrodes ( 6 ,  7 ) and a ceramic insulator ( 3 ) housed in a metal base ( 4 ) which has a base threading ( 5 ), said spark plug ( 1 ) also comprising a lamination cavity ( 15 ) connected to a combustion chamber ( 11 ) included in the internal combustion engine ( 2 ) through a lamination duct ( 16 ) while a lamination injector ( 17 ) can directly or indirectly inject into said cavity ( 15 ) a pilot charge ( 18 ) previously pressurized, said charge ( 18 ) consisting of an combustive-AF fuel mixture easily ignited by a spark, further comprising:
 at least one central electrode ( 6 ) which opens into the lamination cavity ( 15 ); 
 at least one shuttle electrode ( 20 ) which is wholly or partly made of an electrically conductive material and which is partially or entirely housed with a small clearance in the lamination duct ( 16 ), said shuttle electrode ( 20 ) being interposed between the central electrode ( 6 ) and a ground electrode ( 7 ) and having both a chamber-side end ( 21 ) which faces the ground electrode ( 7 ) and which is exposed to the pressure prevailing in the combustion chamber ( 11 ) as well as a cavity-side end ( 22 ) which faces the central electrode ( 6 ) and which is exposed to the pressure prevailing in the lamination cavity ( 15 ), said shuttle electrode ( 20 ) capable of translating into said duct ( 16 ) under the effect of the gas pressure either towards the lamination cavity ( 15 ) when the pressure in the latter is lower than the pressure prevailing in the combustion chamber ( 11 ), or towards the combustion chamber ( 11 ) when the pressure in the latter is lower than the pressure prevailing in the lamination cavity ( 15 ); 
 At least one cavity-side shuttle electrode abutment ( 23 ) which determines the position of the shuttle electrode ( 20 ) closest to the lamination cavity ( 15 ); 
 At least one chamber-side shuttle electrode abutment ( 24 ) which determines the position of the shuttle electrode ( 20 ) closest to the combustion chamber ( 11 ). 
 
     
     
       2. The spark plug with shuttle electrode according to  claim 1 , wherein the shuttle electrode ( 20 ) closes all or part of the lamination duct ( 16 ) when it is closest to the lamination cavity ( 15 ) while opening said duct ( 16 ) over a wider section when it is positioned closest to the combustion chamber ( 11 ). 
     
     
       3. The spark plug with shuttle electrode according to  claim 1 , wherein all or part of the lamination duct ( 16 ) comprises an insulating sleeve ( 25 ) made of an electrically insulating and/or thermally insulating and/or refractory material, which is integral with said conduit ( 16 ), and which is radially and/or axially interposed between the shuttle electrode ( 20 ) and said conduit ( 16 ), said shuttle electrode ( 20 ) being able to translate inside said sleeve ( 25 ). 
     
     
       4. The spark plug with shuttle electrode according to  claim 3 , wherein the insulating sleeve ( 25 ) comprises at least one longitudinal channel ( 35 ) for gas passage which allows the gases to pass from the lamination cavity ( 15 ) to the combustion chamber ( 11 ) or vice versa, said channel ( 35 ) being able to be arranged inside and/or on the inner or outer surface of said sleeve ( 25 ). 
     
     
       5. The spark plug with shuttle electrode according to  claim 1 , wherein the shuttle electrode ( 20 ) consists of an insulating shuttle body ( 26 ) made of an electrically insulating material, said body ( 26 ) being crossed throughout its length by a conductive core ( 27 ) of which it is integral, said core ( 27 ) being made of an electrically conductive material, a first end ( 28 ) of said core ( 27 ) facing the ground electrode ( 7 ) while a second end ( 29 ) of said core ( 27 ) faces the central electrode ( 6 ). 
     
     
       6. The spark plug with shuttle electrode according to  claim 1 , wherein the cavity-side shuttle electrode abutment ( 23 ) consists of a shuttle electrode closing seat ( 30 ) arranged in the lamination duct ( 16 ) or at either end of said duct ( 16 ), said seat ( 30 ) cooperating with a shuttle electrode closing flange ( 31 ) included at the periphery and/or at the end of the shuttle electrode ( 20 ). 
     
     
       7. The spark plug with shuttle electrode according to  claim 6 , wherein the shuttle electrode closing seat ( 30 ) and the shuttle electrode closing flange ( 31 ) form a seal when in contact with each other, said seal preventing any gas from passing through at said point of contact when the pressure prevailing in the combustion chamber ( 11 ) is greater than the pressure prevailing in the lamination cavity ( 15 ). 
     
     
       8. The spark plug with shuttle electrode according to  claim 1 , wherein the chamber-side shuttle electrode abutment ( 24 ) consists of a shuttle electrode opening seat ( 32 ) arranged in the lamination duct ( 16 ) or at either end of said duct ( 16 ), or in the metal base ( 4 ), said seat ( 32 ) cooperating with a shuttle electrode opening flange ( 33 ) included at the periphery and/or at the end of the shuttle electrode ( 20 ). 
     
     
       9. The spark plug with shuttle electrode according to  claim 8 , wherein the shuttle electrode opening seat ( 32 ) and the shuttle electrode opening flange ( 33 ) form a seal when in contact with each other so as to prevent any gas from passing through said contact. 
     
     
       10. The spark plug with shuttle electrode according to  claim 1 , wherein the shuttle electrode ( 20 ) comprises guide means ( 34 ) in its periphery which hold said shuttle electrode ( 20 ) approximately centered in the lamination duct ( 16 ), and approximately in the same longitudinal orientation as said duct ( 16 ) regardless of the axial position of said shuttle electrode ( 20 ) relative to said duct ( 16 ). 
     
     
       11. The spark plug with shuttle electrode according to  claim 1 , wherein the shuttle electrode ( 20 ) comprises at least one longitudinal channel ( 35 ) for gas passage which allows the gases to pass from the lamination cavity ( 15 ) to the combustion chamber ( 11 ) or vice versa, said channel ( 35 ) being arranged inside and/or on the surface of said shuttle electrode ( 20 ) and possibly located either over the entire length of said shuttle electrode ( 20 ) while the two ends of said channel ( 35 ) open respectively at the chamber-side end ( 21 ) and at the cavity-side end ( 22 ), or over a portion only of said length while at least one of said ends of said channel ( 35 ) opens radially from the outer surface of the shuttle electrode ( 20 ). 
     
     
       12. The spark plug with shuttle electrode according to  claim 9 , wherein the cavity-side shuttle electrode abutment ( 23 ) consists of a shuttle electrode closing seat ( 30 ) arranged in the lamination duct ( 16 ) or at either end of said duct ( 16 ), said seat ( 30 ) cooperating with a shuttle electrode closing flange ( 31 ) included at the periphery and/or at the end of the shuttle electrode ( 20 ); and
 wherein the shuttle electrode closing flange ( 31 ) and the shuttle electrode opening flange ( 33 ) form together a single closing-opening flange ( 36 ) which defines with the lamination duct ( 16 )—when said closing-opening flange ( 36 ) is in contact with the shuttle electrode opening seat ( 32 )—a torch ignition prechamber ( 37 ) which communicates simultaneously with both the lamination cavity ( 15 ) as well as the combustion chamber ( 11 ) via at least one gas ejection orifice ( 38 ). 
 
     
     
       13. The spark plug with shuttle electrode according to  claim 12 , wherein all or part of the lamination duct ( 16 ) comprises an insulating sleeve ( 25 ) made of an electrically insulating and/or thermally insulating and/or refractory material, which is integral with said conduit ( 16 ), and which is radially and/or axially interposed between the shuttle electrode ( 20 ) and said conduit ( 16 ), said shuttle electrode ( 20 ) being able to translate inside said sleeve ( 25 ), and wherein the torch ignition prechamber ( 37 ) is arranged inside the insulating sleeve ( 25 ). 
     
     
       14. The spark plug with shuttle electrode according to  claim 13 , wherein the insulating sleeve ( 25 ) protrudes from the metal base ( 4 ) to present a protruding ejection dome ( 47 ) from which the gas ejection orifice ( 38 ) opens. 
     
     
       15. The spark plug with shuttle electrode according to  claim 14 , wherein the protruding ejection dome ( 47 ) is an insert on the insulating sleeve ( 25 ). 
     
     
       16. The spark plug with shuttle electrode according to  claim 14 , wherein the shuttle electrode opening seat ( 32 ) is arranged in the protruding ejection dome ( 47 ). 
     
     
       17. The spark plug with shuttle electrode according to  claim 12 , wherein the inner peripheral wall of the torch ignition prechamber ( 37 ) is cylindrical while the closing-opening flange ( 36 ) is housed at low radial clearance in said prechamber ( 37 ). 
     
     
       18. The spark plug with shuttle electrode according to  claim 6 , wherein when the shuttle electrode ( 20 ) is positioned close to the combustion chamber ( 11 ), that is to say, either in the vicinity or in contact with the chamber-side shuttle electrode abutment ( 24 ) with which it cooperates, the shuttle electrode closing flange ( 31 ) uncovers at least one gas ejection orifice ( 38 ) which connects the lamination cavity ( 15 ) with the combustion chamber ( 11 ). 
     
     
       19. The spark plug with shuttle electrode according to  claim 1 , wherein the lamination injector ( 17 ) can directly or indirectly, via an injector outlet duct ( 42 ), inject the pilot charge ( 18 ) into the lamination cavity ( 15 ) via an annular pilot charge injection chamber ( 39 ) which is arranged either in a threaded spark plug well ( 40 ) into which the metal base ( 4 ) is screwed by means of the base threading ( 5 ), or on the outer periphery of said metal base ( 4 ), or both in said well ( 40 ) and on said periphery of said base ( 4 ), said annular chamber ( 39 ) communicating with the lamination cavity ( 15 ) via at least one gas injection channel ( 41 ) arranged approximately radially in the metal base ( 4 ). 
     
     
       20. The spark plug with shuttle electrode according to  claim 1 , wherein the lamination cavity ( 15 ) is arranged inside the ceramic insulator ( 3 ).